Planetary differential and speed servo

ABSTRACT

A planetary differential employs a longitudinal shaft having a restricted portion at least two balls directly engaging the longitudinal shaft at said restricted portion forming an inner race. The differential includes further an outer race having a taper engaged by the balls and a cage for the balls. A first rotary input is provided to one of the inner race, outer race, and cage. A secondary rotary input is provided to another of the inner race, outer race, and cage. A rotary output is provided to yet another of the inner race, outer race, and cage. The inner race and outer race are mounted for rotary movement. A servo system, including the planetary differential, is also disclosed.

ted States atent U [191 1111 3,768,715 Tout Oct. 30, 1973 [54] PLANETARYDIFFERENTIAL AND SPEED 3,645,430 2/1972 Lagain 226/40 SERVO [75]Inventor: Stanley D. Tout, Arcadia, Calif. Primary Examiner -RichardSchacher Att0rneyl.uc P. Benoit [73] Assrgnee: Bell & Howell Company,Chicago,

111. 22 Filed: May 1, 1972 [57] ABSTRACT A planetary differentialemploys a longitudinal shaft [21] Appl' having a restricted portion atleast two balls directly engaging the longitudinal shaft at saidrestricted por- [52] 11.8. C1. 226/40, 74/796, 226/31, tion forming aninner race. The differential includes 226/44 further an outer racehaving a taper engaged by the [51] Int. Cl B6511 23/18 balls and a cagefor the balls. A first rotary input is [58] Field of Search 226/31, 44,40; provided to one of the inner race, outer race, and 74/797, 801, 798,697, 796 cage. A secondary rotary input is provided to another of theinner race, outer race, and cage. A rotary out- [56] References Citedput is provided to yet another of the inner race, outer UNITED STATESpATENTS race, and cage. The inner race and outer race are 1,399,443 121921 Rennerfelt 74/798 mounted Mary mmemem' 2,974,574 3/1961 Egan 74/796A servo system, including the planetary differential, is 2,996,5838/1961 Springer 226/40 X also disclosed. 3,001,420 9/1961 Juenke l74/798 3,585,878 6/1971 Heckenbach 74/675 20 Claims, 3 Drawing Figuresman r /2EL 33 PLANETARY DIFFERENTIAL AND SPEED SERVO BACKGROUND OF THEINVENTION 1. Field of the Invention The subject invention relates toplanetary differentials and to apparatus for controllably moving anobject.

2. Description of the Prior Art In typical planetary differentialstoothed gears are employed to provide the necessary differentiationbetween inputs and outputs. These gears have numerous disadvantages.They are sensitive to wear and must be inspected often. They haverelatively high frictional losses and, therefore, to obtain a givenoutput, relatively higher inputs must be provided. More importantly,they must be manufactured to close tolerances, and therefore, areexpensive.

In addition, in systems requiring quiet operation, the noise of aplanetary differential employing conventional sun and planet gears withteeth often cannot be tolerated.

In the past, ball hearings were used in speed reducing mechanisms toovercome space limitations. Such a mechanism is shown in IngeniousMechanisms for Designers and Inventors," Vol. IV, Ch. 12, pp. 279-81, byJohn A. Newell and I-Iolbrook L. Horton (Industrial Press, 1967). Itincludes a ball bearing which has one race driven and the other raceconnected to a motor frame. The power output is taken from the ballcage. A dual-input differential action is lacking.

SUMMARY OF THE INVENTION It is an object of the subject invention toovercome the the above mentioned disadvantages.

Another object is to provide an improved planetary differential.

A further object is to provide a system that includes a planetarydifferential for controllably moving an object.

Another object is to maintain a desired object movement by sensingexcessive and insufficient movement of the object and providingcorrective action through a planetary differential.

Other objects of the subject invention will become apparent in thefurther course of this disclosure.

From one aspect thereof, this invention resides in a planetarydifferential comprising in combination a longitudinal shaft having arestricted portion at least two balls directly engaging saidlongitudinal shaft of said restricted portion forming an inner race forthe balls, an outer race for the balls, having a taper engaged by saidballs, a cage for the balls, first rotary input means connected to oneof the inner race, outer race and cage, second rotary input meansconnected to another of the inner race, outer race and cage, rotaryoutput means connected to yet another of the inner race, outer race andcage, and means for mounting the races for rotary movement.

From another aspect thereof, the subject invention resides in anapparatus for controllably moving an object comprising in combination alongitudinal shaft having a restricted portion, at least two ballsdirectly engaging said longitudinal shaft of said restricted portionforming, an inner race for the balls, an outer race for the balls havinga taper engaged by said balls, a cage for the balls, means for mountingthe races for rotary movement, first driving means connected to one ofthe inner race, outer race and cage, second driving means connected toanother of the inner race, outer race and cage, means for coupling theobject for movement to yet another of the inner race, outer race andcage, and means connected to the first driving means for selectivelyenergizing the first driving means.

BRIEF DESCRIPTION OF THE DRAWINGS The invention and its objects willbecome more readily apparent from the following detailed description ofpreferred embodiments thereof, illustrated by way of example in theaccompanying drawings, in which:

FIG. 1 is a side view, partially in section, of an apparatus thatincludes a planetary differential for controllably moving an object inaccordance with a preferred embodiment of the invention;

FIG. 2 is a view taken on the line 22 of FIG. 1;

FIG. 3 is a view of the planetary differential and speed servo in asuggested use in a motion picture projection system.

Like reference numerals in the drawings designate like or functionallyequivalent parts.

DESCRIPTION OF PREFERRED EMBODIMENTS A planetary differential speedservo 10 is shown in FIGS. 1 and 2 as employed in an apparatus thatcontrollably moves a web of material 11. The servo 10 includes aplanetary differential 12 comprising two balls 14 and 15, an inner race17 for the balls, an outer race 18 for the balls, a cage 20 for theballs, and a case 22 for mounting the races for rotary movement.

According to the invention, the inner race 17 takes the form of a shaft(hereinafter referred to as shaft 17 The shaft 17 has a tapered orrestricted portion or groove 24, the bottom 27 of which is curved at aradius slightly larger than the radius of each of the balls 14 and 15.This assures a smooth rolling action of the balls around the shaft 17.As seen in FIG. 1, the shaft has a free end 117 extending into a cavity118 in the outer race 18 which thus provides a bearing for the freeshaft end. The cage 20 is integral with a pulley 25 and contains theballs 14 and 15, maintaining them spaced from each other.

These components are shown in section in FIG. 2. The balls 14 and 15contact the tapered portion 24 of shaft 17. In addition, the ballscontact a tapered portion 28 of the outer race 18.

In FIG. 1, a leaf spring 21 is attached to case 22 by a screw 23. Thespring 21 acts on a ball 26 for thrust loading the shaft 17 toward thebearing formed by the cavity 118 in the outer race 18. This has adesirable effect of loading the balls against the tapered portion 28 ofthe outer race 18. The taper provides mechanical advantage with respectto the loading applied by spring 21. Therefore, by adjusting the degreeof the taper or the force of spring 21, the frictional contact necessaryto drive the outer race 18 is obtained.

A first rotary input is provided through the pulley 25 which is integralwith the cage 20.

In operation, the first rotary input is provided by a belt 32 from amotor 33. The belt drives pulley 25 which is integral with cage 20. Cage20 drives balls 14 and 15 which rotate the outer race 18 by frictionalcontact. The necessary drive friction is achieved by spring 21 whichthrusts loads the shaft 17 against the balls 14 and 15.

A second rotary input is provided by a belt 35 from a motor 36 whichdrives a pulley 30. Pulley 30 is fastened to shaft 17 by a screw 34.Rotation of the shaft 17 causes the outer race 18 to rotate throughfrictional contact with the balls 14 and 15.

Therefore, inputs at pulleys 25 and 30 determine the rotational speed ofthe outer race 18.

Output is taken from the outer race 18 through the shaft 31 which isconnected to the outer race. A roller 40 over which the web of material11 passes is connected to the shaft 31. A roller 41 pinches the web 1 1against roller 40 by means of a bias spring; 43 connected to the rollerarm 44. Thus, the roller 40 serves to drive the web 11.

Those skilled in the art will readily recognize that the subjectinvention is not limited in any of the following respects: Inputs oroutputs may be provided to or taken from either the inner race, outerrace, or the cage. Also, the number of balls employed is limited only bythe physical dimensions of the inner race. And, the inner race need nottake the form of a shaft.

FIG. 3 illustrates a typical projection system in which the planetarydifferential and speed servo may be utilized. The belt 32 (see FIG. 1)drives pulley 25 which is integral with cage 20. Cage drives the balls14 and 15 which rotate the outer race 18, the integral shaft 31, and theroller 40.

Film 51 from a supply reel 52 is pinched between the spring-biasedroller 41 and the drive roller 40. The film is then looped around aroller 61 and into a projector 54. Ratios are designed such that nominalfilm velocity will equal projection (claw or sprocket) speed.

A loop 55 in film 51 must be maintained to provide free claw or sprocketaction, thus isolating the projector proper from supply reel loads. Thisis accomplished by a film tension sensor 60 which comprises acombination the roller 61 around which the loop 55 is formed, an arm 62,a spring 63, and a switch 64 of a polarity reversal type.

If the film supply velocity is too slow, loop 55 will decrease in sizeand arm 62 will pull against spring 63, closing the upper set ofcontacts of switch 64. This causes the magnetic motor 36 to be energizedfrom an electric power source 66 in a rotational direction required tocorrect the film velocity and restore loop 55. The servo motor 36 drivesbelt 35 which rotates pulley 30. Pulley 30 is fastened to shaft 17 whichis in contact with the balls 14 and 15. In turn, the balls 14 and 15drive the outer race 18, integral shaft 31 and roller 40. Therefore, byenergizing the motor 36, a corrective rotary input is added through theplanetary differential to the rotary input supplied by the projectormotor 33. Thus, the outer race 18, and therefore the film drive roller41], is speeded up, allowing the film tension sensor 60 to return to itsnominal position. In this position, the switch 64 is open, and the motor36 is de-energized.

Conversely, if film supply velocity is too fast, the film tension sensor60 acts in the opposite direction and the reverse polarity is applied tothe motor 36 through the lower contacts of switch 64. In this case, thereverse input of the motor 36 through the planetary differential 12would subtract from the input of the projector drive motor 33.Therefore, the result would be a slowing of the speed of film driveroller 40 until the film tension sensor has again returned to itsnominal position.

It should be recognized that although the switch 64 is illustrated as anelectro-mechanical switch, this switch can be one of the proximity types(photo electric or magnetic) that requires no mechanical forcetransmission to actuate.

It should also be noted that the motor 36 is small since it onlyfurnishes power to cancel the speed error in the system. By way ofexample, a magnetic motor, in which a change in polarity will produce achange in rotational direction, may be used. No limitation to magneticor d.c. motors is intended, since other reversible drives may be usedinstead.

In addition, it can be seen that the system is reversible. Reversingprojector drive motor 33 which reverses belt 32 and the direction offilm 51 causes the system to operate in reverse. If the rewind velocityis too slow, loop 55 will increase in size causing the lower set ofcontacts of switch 64 to close. This now energizes motor 36 in such amanner that its rotational input through the planetary differential 12will add to the input of the projector drive motor 33. Therefore, filmdrive roller 40 will increase in speed causing the slack in loop 55 tobe taken up until the film tension sensor returns to its nominalposition.

If the rewind film velocity is too fast, the loop 55 will decrease insize, the upper contacts of switch 64 will close, and the reversepolarity will be applied to motor 36. This causes the film speed todecrease due to the subtractive input of motor 36 through the planetarydifferential, until the film tension sensor again returns to its nominalposition.

It is now readily recognizable that the subject invention overcomes thedisadvantages of conventional planetary gear differentials.Specifically, the balls employed are practically insensitive to wear andmay be hardened and ground using similar methods as for conventionalball bearings. Also, the system has small frictional losses, since itoperates with rolling friction and avoids sliding friction in normaloperation. In addition, the balls and races are easily manufactured, aremuch less expensive than conventional gears, and the complete lack ofmeshing gears provides very quiet operation. Most importantly, very highspeed ratios are attainable between the shaft 17 and the race 18 andcage 20, since the diameter of the shaft 17 may be small relative to thediameter of a corresponding gear wheel in a conventional differentialgear. As one advantage, this saves a stepdown gear stage between theservo motor 36 and the shaft 17.

I claim:

1. A planetary differential comprising in combination:

a longitudinal shaft having a restricted portion;

at least two balls directly engaging said longitudinal shaft at saidrestricted portion forming an inner race for said balls;

an outer race for said balls having a taper engaged by said balls;

a cage for said balls;

first rotary input means connected to one of said inner race, outer raceand cage;

second rotary input means connected to another of said inner race, outerrace and cage;

rotary output means connected to yet another of said inner race, outerrace and cage; and

means for mounting said races for rotary movement.

2. A planetary differential as claimed in claim 1, wherein:

said first rotary input means are connected to said inner race; saidsecond rotary input means are connected to said cage; and said rotaryoutput means are connected to said outer race. 3. A planetarydifferential as claimed in claim 1, wherein:

said planetary differential has only two of said balls. 4. A planetarydifferential as claimed in claim 1, wherein:

said restricted shaft portion is curved and has a radius larger than theradius of each of said balls. 5. A planetary differential as claimed inclaim 1, wherein:

said shaft has a free end and said outer race has a cavity forming abearing for said free shaft end. 6. A planetary differential as claimedin claim 5, including in said combination:

means for biasing said shaft in an axial direction toward said bearingin the outer race. 7. A planetary differential as claimed in claim 6,wherein:

said restricted shaft portion is curved and has a radius larger than theradius of each of said balls. 8. A planetary differential as claimed inclaim 7, wherein:

said planetary differential has only two of said balls. 9. A planetarydifferential as claimed in claim 1, including said combination:

a drive pulley integral with said cage. 10. An apparatus forcontrollably moving an object, comprising in combination:

a longitudinal shaft having a restricted portion; at least two ballsdirectly engaging said longitudinal shaft at said restricted portionforming an inner race for said balls; an outer race for said ballshaving a taper engaged by said balls; a cage for said balls; means formounting said races for rotary movement; first driving means connectedto one of said inner race, outer race and cage; second driving meansconnected to another of said inner race, outer race and cage;

means for coupling said object for movement to yet another of said innerrace, outer race and cage; and

means connected to said first driving means for selec tively energizingsaid first driving means.

11. An apparatus as claimed in claim 10, wherein:

said object is a web of material; and

said means for selectively energizing said first driving means includemeans for sensing excessive and insufficient movement of said web, andmeans connected to said sensing means and to said first driving meansfor selectively energizing said first driving means in a first sense andin a second sense, respectively, in response to sensing of excessive andinsufficient web movement.

12. An apparatus as claimed in claim 11, wherein:

said sensing means include means for sensing the size of a loop of saidweb.

13. An apparatus as claimed in claim 10, wherein:

said first driving means are connected to said inner race;

said second driving means are connected to said cage; and

said coupling means are connected to said outer race.

14. An apparatus as claimed in claim 10, wherein:

said planetary differential has only two of said balls.

15. An apparatus as claimed in claim 10, wherein:

said restricted shaft portion is curved and has a radius larger than theradius of each of said balls.

16. An apparatus as claimed in claim 10, wherein:

said shaft has a free end and said outer race has a cavity forming abearing for said free shaft end.

17. An apparatus as claimed in claim 16, including in said combination:

means for biasing said shaft in an axial direction toward said bearingin the outer race.

18. An apparatus as claimed in claim 17, wherein:

said restricted shaft portion is curved and has a radius larger than theradius of each of said balls.

19. An apparatus as claimed in claim 18, wherein:

said planetary differential has only two of said balls.

20. An apparatus as claimed in claim 10, including in said combination:

a drive pulley integral with said cage.

1. A planetary differential comprising in combination: a longitudinalshaft having a restricted portion; at least two balls directly engagingsaid longitudinal shaft at said restricted portion forming an inner racefor said balls; an outer race for said balls having a taper engaged bysaid balls; a cage for said balls; first rotary input means connected toone of said inner race, outer race and cage; second rotary input meansconnected to another of said inner race, outer race and cage; rotaryoutput means connected to yet another of said inner race, outer race andcage; and means for mounting said races for rotary movement.
 2. Aplanetary differential as claimed in claim 1, wherein: said first rotaryinput means are connected to said inner race; said second rotary inputmeans are connected to said cage; and said rotary output means areconnected to said outer race.
 3. A planetary differential as claimed inclaim 1, wherein: said planetary differential has only two of saidballs.
 4. A planetary differential as claimed in claim 1, wherein: saidrestricted shaft portion is curved and has a radius larger than theradius of each of said balls.
 5. A planetary differential as claimed inclaim 1, wherein: said shaft has a free end and said outer race has acavity forming a bearing for said free shaft end.
 6. A planetarydifferential as claimed in claim 5, including in said combination: meansfor biasing said shaft in an axial direction toward said bearing in theouter race.
 7. A planetary differential as claimed in claim 6, wherein:said restricted shaft portion is curved and has a radius larger than theradius of each of said balls.
 8. A planetary differential as claimed inclaim 7, wherein: said planetary differential has only two of saidballs.
 9. A planetary differential as claimed in claim 1, including saidcombination: a drive pulley integral with said cage.
 10. An apparatusfor controllably moving an object, comprising in combination: alongitudinal shaft having a restricted portion; at least two ballsdirectly engaging said longitudinal shaft at said restricted portionforming an inneR race for said balls; an outer race for said ballshaving a taper engaged by said balls; a cage for said balls; means formounting said races for rotary movement; first driving means connectedto one of said inner race, outer race and cage; second driving meansconnected to another of said inner race, outer race and cage; means forcoupling said object for movement to yet another of said inner race,outer race and cage; and means connected to said first driving means forselectively energizing said first driving means.
 11. An apparatus asclaimed in claim 10, wherein: said object is a web of material; and saidmeans for selectively energizing said first driving means include meansfor sensing excessive and insufficient movement of said web, and meansconnected to said sensing means and to said first driving means forselectively energizing said first driving means in a first sense and ina second sense, respectively, in response to sensing of excessive andinsufficient web movement.
 12. An apparatus as claimed in claim 11,wherein: said sensing means include means for sensing the size of a loopof said web.
 13. An apparatus as claimed in claim 10, wherein: saidfirst driving means are connected to said inner race; said seconddriving means are connected to said cage; and said coupling means areconnected to said outer race.
 14. An apparatus as claimed in claim 10,wherein: said planetary differential has only two of said balls.
 15. Anapparatus as claimed in claim 10, wherein: said restricted shaft portionis curved and has a radius larger than the radius of each of said balls.16. An apparatus as claimed in claim 10, wherein: said shaft has a freeend and said outer race has a cavity forming a bearing for said freeshaft end.
 17. An apparatus as claimed in claim 16, including in saidcombination: means for biasing said shaft in an axial direction towardsaid bearing in the outer race.
 18. An apparatus as claimed in claim 17,wherein: said restricted shaft portion is curved and has a radius largerthan the radius of each of said balls.
 19. An apparatus as claimed inclaim 18, wherein: said planetary differential has only two of saidballs.
 20. An apparatus as claimed in claim 10, including in saidcombination: a drive pulley integral with said cage.